Such multi-carrier systems often implement Orthogonal Frequency Division Multiplexing (OFDM) as multi-carrier transmission technique. OFDM is for example used in the HIPERLAN/2 standard as well as an extension of the IEEE 802.11a standard for the 5 Ghz area. OFDM could also offer a sensible alternative for high-speed mobile applications, and thus represents an important step for next generation mobile radio systems or for a 4th generation air interface. To this extend, the 3rd Generation Partnership Project (3GPP), for the standardization of high-speed broadband wireless mobile communication systems, is recently considering the application of OFDM techniques for the high speed data packet access (HSDPA) air interface communication between the radio access network (RAN) and the user equipment (UE).
In multi-carrier systems as OFDM transmission system, the transmitted data is split into a number of parallel data streams, each one used to modulate a separate sub-carrier. In other words, the broadband radio carrier is subdivided into a plurality of narrow-band subcarriers or sub-carriers being independently modulated with e.g. QPSK, 16 QAM, 64 QAM or higher modulation order allowing higher data rate per sub-carrier.
In such OFDM systems, the sub-carrier frequencies can be allocated to a user carrier on a short term basis (e.g. all 2 ms) as well the modulation order per sub-carrier defining a transmission carrier for each user should be updated on the same short term basis.
A very important task of such multi carrier systems to provide for an efficient sub-carrier/modulation allocation to the different users. This is necessary to optimize and extend the performance of the multi-carrier system.
The selection of the best appropriate sub-carrier for each user should take into account that in mobile environment with multipath radio carriers some sub-carriers may be subject to very strong carrier attenuation when seen by a given user. Such sub-carriers would be uselessly allocated to this user because of fading. On the contrary, they may be received with good quality by other users.
The selection of the sub-carriers to be used between a base station and a UE should be coordinated between the transmitter and the receiver to avoid errors. In prior art, a message indicating the sub-carriers to be used is exchanged between the transmitter and the receiver in the feed forward carrier i.e. on the same carrier to be used for transmitting user data and prior to the transmission of the user data. This kind of signaling information consumes a not negligible bandwidth and time so that the effective payload data rate is reduced accordingly.
The message containing the sub-carriers to be used represents a huge amount of signaling information (some 100 Kbits) especially in multi carrier system with up to thousand sub-carriers.
A particular object of the present invention is to provide a method for sending information on the sub-carriers to be used between a transmitter and a receiver in a more efficient way so that the amount of signaling information in the feed forward carrier is reduced but anyway sufficient for performing an efficient resource allocation in the multi carrier system.
Another object of the invention is to provide a corresponding receiver.